Endovascular therapy using a high-performance catheter such as a balloon catheter and a stent has been performed. An imaging apparatus for diagnosis such as an optical coherence tomography (OCT) apparatus is generally used for pre-operative diagnosis and post-operative follow-up.
The optical coherence tomography apparatus can include a built-in optical fiber in which an imaging core having an optical lens and an optical mirror is attached to a distal end thereof, and uses a probe having a sheath in which at least a distal end portion is transparent. The probe is guided to the inside of a blood vessel of a patient, and while the imaging core rotates, a blood vessel wall is irradiated with light via the optical mirror. Radial scanning is performed by receiving reflected light again from the blood vessel wall via the optical mirror, thereby constructing a cross-sectional image of the blood vessel based on the obtained reflected light. A three-dimensional image of a lumen surface of a blood vessel in a longitudinal direction can be formed by rotating the optical fiber and performing a pulling operation (generally, referred to as pulling-back) at a predetermined speed (JP-A-2007-267867). In addition, as an improved OCT, a swept-source optical coherence tomography (SS-OCT) apparatus has been developed.
Incidentally, light is attenuated and scattered in blood so that scanning of a vascular lumen surface performed by transceiving optical signals is hindered. Therefore, normally, when performing scanning, flushing liquid in which light is unlikely to be attenuated and scattered is released through a guiding catheter, and the inside of a blood vessel is filled with the flushing liquid, thereby ensuring optical transparency. The operation is literally referred to as a flushing operation. As the representative flushing liquid, there are an isotonic solution such as saline, an angiography contrast agent, and mixed liquid thereof. Here, the optical refractive index of the flushing liquid varies depending on the type, or the ratio of mixing rate.
In a case of an optical coherence tomography apparatus, light output from a light source inside the apparatus is divided into measurement light and reference light, and the measurement light is emitted toward a vascular tissue. Reflected light (scattered light) from the vascular tissue is received, and interference light with respect to the reference light reflected while being separated by a predetermined distance is obtained. Thus, a blood vessel tomographic image is reconstructed based on the intensity thereof. Therefore, in a case where the refractive index of the flushing liquid varies as described above, the space distance in liquid (calculated based on the optical path difference with respect to the reference light, and the refractive index) changes. Accordingly, the refractive index of the flushing liquid used during pull-back scanning becomes an important parameter when performing reconstruction of a blood vessel cross-sectional image.
Here, there is a case where the flushing liquid utilized when performing the pull-back scanning is forgotten, thereby resulting in problems. If proper flushing liquid can be designated, it also denotes that a proper refractive index can be designated. Therefore, it is possible to maintain a highly accurate scale (measurement) of a blood vessel cross-sectional image to be reconstructed. Meanwhile, in a case where a user erroneously designates the flushing liquid, the scale of the reconstructed blood vessel cross-sectional image becomes different from the original scale, thereby leading to an erroneous diagnosis.